1. Field of the Invention
The present invention relates to a method of mounting a semiconductor chip part having a plurality of pads on a substrate having a plurality of lands.
2. Description of the Related Art
A plurality of pads which are conductive electrodes for connection are formed on a semiconductor chip part to be mounted, and lands which are formed in a conductive wiring pattern correspondingly to the pads are formed on a substrate to be formed with the semiconductor chip part.
For example, there have been known two method of mounting a semiconductor chip part on a substrate. One methods involves contact-bonding a gold wire on each of pads formed on a semiconductor chip part by a bonding tool, followed by tearing of the gold wire, to form on each pads a two-step bump having an upper step portion in the vicinity of a portion from which the gold wire is torn and having a relatively small volume and a lower step portion expanded by contact-bonding and having a relatively large volume.
In the above method, the bumps formed on the pads are individually brought in press-contact with part of the bonding tool or a specialized tool having a flat surface in sequence, so that the whole of the upper step portions and the lower step portions of the bumps are plastically deformed, to be thus flattened. The semiconductor chip part thus formed with the bumps is adhesively bonded on the substrate using an adhesive of a thermosetting type or a ultraviolet-ray hardening type in a state in which the pads are aligned with lands formed on the substrate correspondingly to the pads.
Another method of mounting a semiconductor chip part on a substrate involves placing metal balls in reverse taper holes of a mold, mounting a substrate having lands on the mold from top, and pressurizing the substrate onto the mold, to contact-bond the metal balls on the lands by plastically deforming the whole of the metal balls by the mold, thereby forming taper bumps on the lands. The semiconductor chip part having the pads is adhesively bonded on the substrate formed with the bumps by an adhesive of a thermosetting type or a ultraviolet-ray hardening type in a state in which the pads are aligned with the corresponding lands.
According to the former prior art method, since portions of the bumps are individually flattened in sequence, there occurs a problem that it takes a lot of time for the flattening work and also it is difficult to make heights of the bumps equal to each other; and since not only the upper step portions but also the lower step portions of the bumps are plastically deformed at the step of flattening the bumps, there occurs another problem that the bumps allow only slight margins for deformation when the semiconductor chip part is pressurized on the substrate, to thereby reduce a reliability in connection between the pads and lands through the bumps additionally in consideration of the uneven heights of the bumps.
According to the latter prior art method, since the metal balls are placed in the taper holes of the mold, there occurs a problem that the metal balls may be possibly lost by vibration of the mold, etc. and there is a limitation of the posture upon pressing work; and since the whole of the metal balls are plastically deformed at the step of forming the taper bumps, there occurs a problem that the bumps allow only slight margins for deformation at the subsequent step of pressurizing the semiconductor chip part on the substrate, to thereby reduce a reliability in connection between the pads and lands through the bumps.
An object of the present invention is to provide a method of mounting a semiconductor chip part on a substrate, which is capable of realizing high efficiency and high reliability of the mounting works.
In accordance with an aspect of the present invention, there is provided a method of mounting a semiconductor chip part on a substrate, including the steps of: flattening conductive bumps formed on a plurality of pads of the semiconductor chip part by bringing the conductive bumps in press-contact with a flattening tool member; and pressurizing the semiconductor chip part on the substrate in a state in which the pads are aligned with lands of the substrate corresponding to the pads; wherein a pressurizing force applied at the pressurizing step is larger than a press-contact force applied at the flattening step.
In the mounting method having the above configuration, since a pressurizing force at the pressurizing step is set to be larger than the press-contact force at the flattening step, only part of the bumps are plastically deformed at the work of flattening the bumps and the whole of the bumps are plastically deformed when the semiconductor chip part is pressurized on the substrate, to make larger margins of the bumps for deformation when the semiconductor chip part is pressurized on the substrate. This makes it possible to closely join the bumps to the corresponding lands and hence to increase a reliability in connection between the pads and the lands through the bumps.
In accordance with another aspect of the present invention, there is provided a method of mounting a semiconductor chip part on a substrate, including the steps of: attracting conductive ball members in through-holes of a mask member, each of the through-holes having a diameter smaller than that of each of the ball members; and forming bumps by aligning the ball members with pads of the semiconductor chip part and pressurizing the ball members onto the pads; wherein a pressurizing force applied at the bump forming step is set at a value capable of forming a flat portion on each of the ball members by a ball member attracting surface of the mask member.
In the mounting method having the above configuration, since the ball members are attracted into the through-holes of the mask member and the mask member in such a state is pressurized on the semiconductor chip part, it becomes possible to reduce frequencies of accidents that the ball members are lost and to alleviate the limitation of the posture upon pressing work; and since the pressurizing force is substantially set at a value capable of forming a flat surface on part of each bump at the step of forming the bumps in order to plastically deform only part of the bump, to make larger margins of the bumps for deformation when the semiconductor chip part is pressurized on the substrate. This makes it possible to closely join the bumps to the corresponding lands and hence to increase a reliability in connection between the pads and the lands through the bumps.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.